The invention relates to calorimeters, e.g., microcalorimeters, and calorimetry methods.
Microcalorimeters are devices that measure very small quantities of heat. In chemistry, biochemistry, cell biology, and pharmacology, ultrasensitive microcalorimeters are frequently used to measure thermodynamic properties of biological macromolecules, such as proteins.
A typical microcalorimeter has two cells, a “reference cell” filled with a liquid, and a “sample cell” filled with a dilute solution of a test substance, e.g., a macromolecule, in the same liquid. By comparing the heat evolved or absorbed by the two cells in response to changes in certain stimuli, such as temperature or concentration of a ligand, information about the test substance can be determined.
There are generally two popular types of microcalorimeters: the differential scanning calorimeter and the isothermal titration calorimeter. The differential scanning calorimeter automatically raises or lowers the temperature of the system at a given rate, while monitoring any temperature differential that arises between the two cells. From the temperature differential information, small differences between the amount of heat absorbed or released by the sample cell in comparison to the reference cell can be determined and attributed to the test substance.
In isothermal titration calorimetry, the instrument maintains a constant temperature while the concentration of an additional substance added to the cells is varied. The additional substance can be, e.g., a ligand that binds to the test substance in the sample cell. The instrument measures the heat absorbed or released as the newly introduced ligand binds to the test substance. By repeating the titration experiment using multiple additions of the ligand until binding is complete, various information concerning the interaction between the test substance and the ligand, e.g., stoichiometry, binding constant, and heat of binding, can be determined.